It has heretofore been proposed to provide a cased glass stream for forming glassware having layered wall segments. U.S. application Ser. Nos. 08/374,371 now abandoned (refiled as Ser. No. 08/787,061, now U.S. Pat. No. 5,776,221) and 08/374,372 now abandoned (refiled as Ser. No. 08/782,552), both assigned to the assignee hereof, disclose techniques for delivering such a cased glass stream in which core glass from a first source is delivered through a first orifice. A second orifice is vertically spaced beneath and aligned with the first orifice, and is surrounded by an annular chamber that communicates with the second orifice through the gap between the first and second orifices. A heated tube delivers casing glass from a second glass source to the annular chamber that surrounds the second orifice. Glass flows by force of gravity from the first and second sources through the first and second orifices in such a way that a cased glass stream emerges from the second orifice. This cased glass stream may be sheared by conventional techniques to form individual cased glass gobs for delivery to conventional individual section glassware forming machines.
Although the techniques disclosed in the noted patent applications address and overcome problems theretofore extant in the art, further improvements remain desirable. For example, since the casing glass layer is relatively thin, it is necessary that the casing glass delivery mechanism be capable of delivering glass at very low pull rates, such as on the order of five to ten tons per day. Furthermore, the casing glass delivery spout must be capable of arresting flow for an extended period of time, such as up to forty-five minutes during installation and start-up, without the flow control tube becoming frozen to the bottom of the spout. It has been proposed in the above-noted applications to provide an array of gas burners within the casing glass spout above the glass pool for both convection and radiant heating of the glass pool in an effort to maintain an elevated glass temperature. These prior art constructions operate satisfactorily during normal operation, but are not as efficient as desired during start-up or periods of non-use. It is therefore a general object of the present invention to provide a method and apparatus of the described character for delivering a cased glass stream in which the casing glass delivery spout is adapted to deliver glass at very low pull rate, including a zero flow pull rate, for an extended period of time without freezing or malfunction.
In general, the foregoing and other objectives of the present invention are accomplished by configuring the casing glass delivery spout for improved heat transfer to, and improved heat retention within, the casing glass pool or bath within the spout. To accomplish this, a number of structural and functional improvements are implemented as compared with conventional glass spout designs. Specifically, in a casing glass spout having one or more spout tubes for controlling glass flow through one or more spout openings, the ratio of the glass pool surface area occupied by the spout tube(s) to the actual overall casing glass pool surface area is not more than 15%, more preferably not more than 10%, and most preferably about 8%. This enlarged glass pool surface area, as compared with ratios on the order of 25% to 27% in conventional spout designs, promotes heat transfer into the glass pool, both directly from the gas burners and from the radiant walls of the spout and covers above the glass pool. Depth of the glass pool is also reduced as compared with conventional spouts to promote heat transfer from the pool surface through the pool to the glass surrounding the spout opening. The ratio of pool surface area to pool depth in the preferred embodiments of the invention is at least 50/1, and more preferably at least 75/1, as compared with conventional ratios on the order of 28/1 to 32/1.
Furthermore, in accordance with another aspect of the present invention, the free space above the glass pool is enlarged so as to provide more volume for gas combustion without contact of gas flames with the pool surface, and a greater area for heat transfer by radiation from the spout sidewall and cover to the surface of the glass pool. The number of gas burner ports is increased for additional heat transfer into the glass pool. The housing that supports the casing glass spout is designed such that an annular spout support surface engages the spout radially outwardly of the spout opening(s) for reducing heat transfer from casing glass flowing through the opening. Increased insulation is disposed between the outer wall surface of the casing glass spout and the inner wall surface of the housing for further reduction of heat transfer.